1. Field of the Invention
The present invention generally relates to devices for launching and receiving a body within a pipeline. More particularly, this invention relates to an end coupling for a pipeline through which a "pig" is inserted and removed, wherein the coupling facilitates insertion and removal of the pig and reduces the labor necessary to gain access to the pipeline through the coupling.
2. Description of the Prior Art
Under certain circumstances, a pipeline used to carry fluids must be cleaned or otherwise cleared of residual fluids and/or contaminants in order to avoid contamination of a fluid that will later be carried by the pipeline. There is also the occasion where two different fluids are to be flowed in succession through a single pipeline, necessitating that the fluids be prevented from mixing during transport. On such occasions, a body having an outer diameter closely matching the inner diameter of the pipeline is inserted and then "launched" within the pipeline. The body, referred to in the industry as a "pig," is typically spherical or cylindrical in shape, and is forced through the pipeline by the fluid flowing therethrough. Near the intended destination for the fluid, the pig is "received" in a manner that permits the fluid following the pig to continue downstream through the pipeline and on to its destination. If appropriately shaped and equipped, the pig can perform the function of cleaning debris or various contaminants from the pipeline, clear a pipeline of residual fluids from a previous operation, or separate two fluids flowing simultaneously through the pipeline. Pigs have been adapted for large pipelines, such as those carrying natural gas and oil across long distances, as well as pipelines within a single processing facility or plant.
To insert or remove a pig from a pipeline, coupling joints are required through which access is gained to a section of the pipeline where the pig can be launched or has been received, respectively. A basic approach is to equip the opposite ends of a pipeline with a pair of terminals, referred to as launcher/receivers. Each launcher/received is configured with a recess sized to accommodate the pig, and generally enables the pig to be launched into and received from the fluid flowing through the pipeline near the launcher/receiver. A standard flanged cover serves as a closure through which the pig can be inserted and removed from the launcher/receiver. However, bolts necessary to secure the flange cover to the launcher/receiver require removal and replacement each time a pig is inserted and removed, making the task somewhat labor intensive. Furthermore, if residual pressure remains within the pipeline, the operation can be hazardous to the worker and those nearby. Finally, the pig may not be readily retrievable from the pipeline after the cover is removed, depending on the shape and size of the pig. Accordingly, launcher/receivers equipped with conventional flanged covers must at times be positioned vertically below the pipeline in order gain the assistance of gravity to extract the pig from the pipeline.
Due to the aforementioned shortcomings, the industry has proposed various couplings that facilitate pig launching and receiving. Examples include U.S. Pat. No. 4,073,303 to Foley, Jr., and U.S. Pat. No. 4,237,936 to Lollis et al. Notably, the pig launcher/receivers disclosed by Foley, Jr. and Lollis et al. are configured to relieve residual pressure in a pipeline, thereby promoting operator safety when removing a pig. Each also is configured to simplify the operation of inserting and removing a pig from a pipeline. However, these launcher/receivers require the assistance of gravity to launch and receive pigs through a vertical passage. Furthermore, each of these launcher/receivers has a somewhat complicated construction, and neither is adapted for a pig having other than a spherical shape.
Accordingly, it would be desirable to provide a pig launcher/receiver that is not only able to safely vent residual pressure in a pipeline when used to remove a pig, but also has an uncomplicated construction and operation, facilitates removal of a pig without the assistance of gravity, and is versatile as to the type of pig that can be launched and received.